Abstract

Sustainable use refers to exploiting a resource so that the resource is not depleted or permanently damaged. Sustainability
is an internationally accepted minimal goal in managing biological resources. However, many populations are managed under
more stringent goals, for example obtaining maximum sustainable biological or economic yield. Overexploitation refers to exploitation
that is more intensive than such specific goals. While overexploitation is not sensible from societal point of view, in practice
overexploitation often occurs because of the conflicting interests between individual exploiters and the public, and because
individual exploiters often are maximizing short rather than long‐term benefits. When sustainable exploitation is attempted,
significant practical challenges remain in determining particular exploitation levels that would guarantee chosen management
goals. Good intentions may be ruined if uncertainty is not properly accounted for, and overexploitation may also result from
lack of precaution.

(a) The relationships between exploitation effort, equilibrium population abundance and equilibrium yield in the logistic
single‐species model. For too high effort, population goes extinct. The dependence between effort and yield is dome‐shaped,
with the maximum sustainable yield (MSY) obtained in the middle. Sustainability declines with effort, but threshold beyond which exploitation is ‘unsustainable’
is a matter of debate. Similarly, the threshold for ‘overexploitation’ is a matter of debate. In this example, it is assumed
that obtaining MSY is the management objective, and that effort levels that are higher than one giving MSY are considered biological overexploitation. Economic yield is usually maximized at a lower effort than biological yield.
Consequently, economic overexploitation may be scored even when biological overexploitation is not yet occurring. While the
detailed relationships depicted here depend on the model, the overall picture is model‐independent. (b) Dynamics of unexploited
and exploited population in the logistic model. Unexploited population reaches carrying capacity (thick black curve). If exploitation
is started, abundance declines. In the logistic model, intermediate effort (thick grey curve) gives the highest sustainable
yield, but this also results in substantial reduction in equilibrium abundance. Notice that overexploitation (thin black curve)
gives higher initial yield than exploiting with effort giving MSY.

Figure 2.

Number of species extinct or threatened by harvesting according to IUCN Red List. This includes hunting and gathering for food, medicine, fuel, material and cultural, scientific and leisure activities.
No marine or freshwater plant species were listed. Data from the International Union for Conservation of Nature and Natural
Resources (IUCN; http://www.iucnredlist.org/, accessed in March 2008).

Figure 3.

State of the world marine fish stocks (FAO, ). FAO started monitoring the world's fish stocks in 1974, and categorizes them in different groups based on the level they have
been exploited (see figure legend). The percentage of stocks ‘underexploited’ or ‘moderately harvested’ has decreased while
the percentage of stocks ‘fully’ or ‘overexploited’ has increased. Underexploited and moderately exploited stocks could produce
higher sustainable yields if exploited more, whereas fully exploited stocks are producing catches that are at or close to
their maximum sustainable limits. Overexploited, depleted and recovering stocks are yielding less than their maximum potential
owing to excess fishing pressure, with no possibilities in the short or medium term of further expansion. Reproduced from The State of World Fisheries and Aquaculture (2006), with permission from the Food and Agriculture Organization
of the United Nations.

The United Nations
(1982) United Nations Convention on the Law of the Sea (http://www.un.org/Depts/los/index.htm).

The United Nations
(1992) Convention on Biological Diversity (http://www.cbd.int/convention/convention.shtml).

The United Nations
(2002) Plan of Implementation of the World Summit on Sustainable Development. A/CONF.199/20, Chapter 1, Resolution 2, Johannesburg, September 2002 (http://www.un‐documents.net/jburgpln.htm).